The seismic sequences of December 2015 (ML= 4.3) and May 2016 (ML = 4.9) in Guadalajara, Jalisco, México.

Historically, the city of Guadalajara has been affected not only by great regional earthquakes (M > 7.0) associated with the subduction process and regional crustal structures but also by local seismic sequences, that caused moderate to severe structural damage to buildings, whose source is not clear. Between December 2015 and May 2016, two seismic sequences occurred, affecting the city of Guadalajara. Both seismic sequences were recorded by the Jalisco Seismic Accelerometric Telemetric Network. The preliminary locations for May 2016 sequence estimated by the Antelope automatic system show alignment with an NNE-SSW trend, west of the city of Guadalajara. The subsequent relocations of theses earthquakes show two N–S alignments at the west of the city of Guadalajara, which agree with December 2015 hypocenters. The focal mechanisms analysis of the earthquakes shows that most of them correspond to normal fault mechanisms that are parallel to the hypocentral alignments suggesting the existence of two active faults responsible for the seismic sequences. Furthermore, these structures might constitute a graben, which we refer to as Zapopan Graben. Additionally, we calculated that these faults are 21 and 28 km length, respectively, which indicates that could have the potential to generate shallow earthquakes that reach magnitudes of 6.2 and 6.5, and could cause significant damages in the Guadalajara Metropolitan Zone. • We analyze the first seismic data set of a seismic sequence in Guadalajara (GMZ), registered by close seismic stations. • Two active normal faults are identified using the seismicity data suggesting the existence of a local graben at GMZ. • The results of this study indicate that the seismic hazard in the GMZ should be reevaluated. • A review was carried out, as complete as possible, of the historical seismicity in the Jalisco Block region. [ABSTRACT FROM AUTHOR]